Small-sized portable devices are widespread worldwide these days, and at the same time demand for small-sized and large-capacity nonvolatile memory is rapidly expanding with significant progress in high-speed information transmission network. In particular, NAND flash memory and small-sized HDD (hard disk drive) have made rapid progress in recording density and form a big market.
Under such a situation, some ideas of new memory that aim to greatly exceed the limit of recording density are proposed. As one of them, a phase-change nonvolatile memory device (phase-change memory) (PCRAM: phase-change random access memory) is investigated. The phase-change nonvolatile memory device is a nonvolatile memory device utilizing the property that a phase-change film changes between a crystal state and an amorphous state by applying an electric field pulse to the phase-change film. By reversibly changing the phase-change film between a high resistance state (amorphous state, OFF) and a low resistance state (crystal state, ON), information is stored so that the information can be rewritten and may not be erased even if the power supply is cut. Nonvolatile properties are achieved because both the high resistance state and the low resistance state of the phase-change film are stable. The readout is performed by passing a readout current that is small enough not to cause the writing/erasing through the recording material and measuring the electric resistance of the recording material.
In regard to the phase-change nonvolatile memory device, it is desirable to further increase the operating speed of the writing and the like. As to this, a nonvolatile memory device is reported that includes: a lower electrode; an upper electrode; a recording layer provided between the lower electrode and the upper electrode and containing a phase-change material; and a block layer capable of blocking the phase change of the recording layer (JP-A 2007-194586 (Kokai)). The following is described in this document: since the device includes the block layer capable of blocking the phase change of the recording layer, the heat release toward the upper electrode is suppressed, and the phase change region at the time when a writing current is applied is significantly limited; and this enables to provide high heat generation efficiency, which can achieve not only less writing current but also higher writing speed than in the past.